Method and System for Data Synchronization

ABSTRACT

A system for monitoring includes: multiple EEG sensors spatially positioned on a layer of tissue for capturing EEG signals of a patient; multiple amplifiers coupled with the EEG sensors for amplifying the captured signals; and a low frequency oscillator for generating a synchronizing signal which is distributed to the amplifiers for synchronizing the digitization of the captured signals; wherein each amplifier includes: a voltage controlled oscillator for an adjustable frequency reference; an analog to digital converter for converting the amplified signal to a digital value; and a microcontroller for controlling the frequency of the voltage controlled oscillator and operation of the analog to digital converter by using the synchronizing signal.

CROSS REFERENCE

The present application is a division application of U.S. patentapplication Ser. No. 16/667,570, entitled “Method and System for DataSynchronization” and filed on Oct. 29, 2019, which relies on U.S. PatentProvisional Application No. 62/752,675, of the same title and filed onOct. 30, 2018, for priority, both of which are herein incorporated byreference in their entirety.

FIELD

The present specification generally relates to the field ofneuro-monitoring applications and more specifically to a system andmethod for synchronizing multiple amplifiers being used in conjunctionfor amplifying captured electroencephalography (EEG) signals and otherbiopotential signals.

BACKGROUND

Several medical procedures involve deploying multiple sensors on thehuman body for the recording and monitoring of data required for patientcare. Information, such as vital health parameters, cardiac activity,bio-chemical activity, electrical activity in the brain, gastricactivity and physiological data, is usually recorded through on-body orimplanted sensors/electrodes which are connected through a wired orwireless link. Typical patient monitoring systems comprise a controlunit connected through a wire to one or more electrodes coupled to thespecific body parts of the patient. In some applications, such as withpulse oximeter or EKG (electrocardiograph) devices, the electrodescoupled to the body are easily managed as there are not too many.However, with procedures that require a large number of electrodes to becoupled to the human body, the overall set up, placement and managementof electrodes is a cumbersome process.

One such procedure that requires a large number of electrodes is LongTerm Electroencephalography (EEG) Monitoring (LTM). The purpose of LTMis to detect abnormal brain activity. The presence of abnormal brainactivity may require medications and/or surgical interventions. Duringsurgical procedures, LTM may reduce the risk to the patient ofiatrogenic damage to the nervous system, and/or to provide functionalguidance to the surgeon. Generally, neuromonitoring procedures such asEEG involve a large number of electrodes coupled to the human body. Inan EEG procedure, the electrodes are used to record and monitor theelectrical activity corresponding to various parts of the brain fordetection and treatment of various ailments such as epilepsy, sleepdisorders, tumors and coma. EEG procedures are either non-invasive orinvasive. In non-invasive EEG, a number of surface electrodes aredeployed on the human scalp for recording electrical activity inportions of the underlying brain. In invasive EEG, through surgicalintervention, the electrodes are placed directly over sections of thebrain, in the form of a strip or grid, or are positioned in the deeperareas of the brain in the form of a depth electrode. All of theseelectrode types are coupled to a wire lead which, in turn, is connectedto a medical system adapted to receive and transmit electrical signals.The electrical activity pattern sensed by various electrodes is analyzedusing standard algorithms to localize or spot the portion of brain whichis responsible for causing the specific ailment.

The number of electrodes in EEG systems typically varies between 21 and256. Increasing the number of electrodes in EEG procedures helpsdecrease the localization error and thus more ably assist the physicianto better plan for surgical procedures. Accordingly, advanced EEGsystems involve a high density electrode configuration with more than256 electrodes, possibly 1024 electrodes, for separately mapping theelectrical activity corresponding to every portion of the brain.However, the overall set up and verification process becomes more timeconsuming and error prone as the number of electrodes increases in theEEG procedures.

Most EEG monitoring systems comprise an amplifier for amplifying anddigitizing the recorded signals before analyzing the signals. In EEGsystems consisting of more than one amplifier, the data from eachamplifier must be time synchronized with each other. Datasynchronization is important since cerebral events such as seizures havea temporal significance and the EEG signals recorded from a patient maybe acquired by more than one amplifier, as is the case in high channelcount intracranial EEG monitoring systems. Also, any difference insample rate between the amplifiers will result in beat frequency noisewhen the EEG channels in one amplifier are fed as reference to the EEGchannels of another amplifier. Beat frequency noise is a periodicartifact added to the EEG signal and is a result of one amplifier'sdigitizer's (ADCs) sampling a common mode noise of another amplifier asa differential signal. The noise may inhibit analyzing the EEG signals.

Known methods of synchronizing multiple amplifiers include runningmultiple synchronizing clocks and signals from one amplifier to anotheror using high precision temperature controlled oscillators in each ofthe amplifiers, the latter of which requires extremely stable clockoscillators that are typically temperature controlled and an order ofmagnitude higher in cost than a voltage controlled oscillator, requiremuch more power than a voltage controlled oscillator, and are alsophysically much larger in size.

The other method of synchronizing the data from different amplifierscomprises sharing the sample clocks of the amplifiers and sharing the‘convert start’ signals among all the analog to digital converters (ADC)of all the amplifiers. Though it is possible to share such signalsbetween all of the amplifiers, this is not a desirable topology becausespecialized and high current consumption equipment and cables would berequired to do so and also because the ADC signals can be corrupted byelectromagnetic interference, resulting in unexpected functioning of theADCs.

Hence what is needed is a less complex method of synchronizing the dataacquisition from multiple amplifiers than that provided by prior art.What is also needed is a method of synchronization that does not requirespecialized components, is cost effective and is not susceptible tointerference from electrostatic discharge (ESD) interference, electricfast transient (EFT) interference, or other electromagneticinterferences. Such a method would preferably eliminate the need fordistributing data from a high speed clock to each of the amplifiers.Distribution of high speed clock data between amplifiers is notdesirable since this requires differential circuitry and cabling, and issusceptible to interference from ESD, EFT, and other electromagneticinterference.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods, which aremeant to be exemplary and illustrative, and not limiting in scope. Thepresent application discloses numerous embodiments.

The present specification discloses a system for monitoring EEG signalscomprising: a plurality of EEG sensors positioned on a layer of tissuefor capturing EEG signals of a patient; at least one amplifier coupledto each of the plurality of EEG sensors, wherein the at least oneamplifier is configured to amplify the captured EEG signals; and a firstoscillator configured to generate a synchronizing signal; wherein the atleast one amplifier comprises: an input for receiving the synchronizingsignal transmitted from the first oscillator; a second oscillator; ananalog to digital converter coupled with the second oscillator andconfigured to digitize the captured EEG signals; and a microcontrollerconfigured to control a frequency of the second oscillator and anoperation of the analog to digital converter (ADC) based on thesynchronizing signal.

Optionally, the first oscillator is configured to generate thesynchronizing signal having a frequency in a range of 0.1 Hz to 10 kHz.

Optionally, the second oscillator is voltage controlled.

Optionally, the plurality of EEG sensors are configured to monitorintracranial EEG signals.

Optionally, the system further comprises a computing device in datacommunication with the plurality of amplifiers for processing theamplified EEG signals. Optionally, the system further comprises adisplay in data communication with the computing device for displayingthe amplified EEG signals.

Optionally, the input comprises a signal isolator configured to receivethe synchronizing signal. Optionally, the signal isolator comprises oneor more isolated DC-DC power converters.

Optionally, the synchronizing signal has a frequency of 1 Hz.

Optionally, the microcontroller comprises a digital to analog (DAC)converter and the microcontroller is configured to adjust the secondoscillator by setting the DAC to a corresponding voltage.

Optionally, the at least one amplifier further comprises an internaltimer and the microcontroller is configured to measure the period of thesynchronizing signal using the internal timer. Optionally, the internaltimer has a resolution in a microsecond numerical range.

Optionally, the at least one amplifier further comprises a filterconfigured to filter out high frequency noise present in an analogvoltage transmission from the microcontroller, wherein the highfrequency noise has a frequency greater than 2 kHz.

Optionally, the at least one amplifier comprises at least one uniqueamplifier in dedicated data communication with each of the plurality ofEEG sensors.

The present specification also discloses a method for synchronizing EEGsignals measured by an EEG monitoring system, wherein the EEG monitoringsystem comprises a plurality of EEG sensors positioned on a layer oftissue and wherein each of the plurality of EEG sensors is configured tocapture EEG signals of a patient, at least one amplifier coupled to eachof the plurality of EEG sensors and configured to amplify the capturedEEG signals, and a first oscillator, wherein the at least one amplifiercomprises an input for receiving a synchronizing signal from the firstoscillator, the method comprising: distributing the synchronizing signalfrom the first oscillator to each of the at least one amplifier;measuring a period of the synchronizing signal; adjusting a secondoscillator, having a frequency, in the at least one amplifier to match atimer count based on the period of the synchronizing signal; determininga function of the frequency of the second oscillator frequency toproduce a clock signal; and adjusting a frequency of each of the secondoscillators such that the frequencies of the second oscillators areidentical.

Optionally, the first oscillator is configured to generate thesynchronizing signal having a frequency in a range of 0.1 Hz to 10 kHz.

Optionally, the second oscillator is voltage controlled.

Optionally, the function of the frequency of the second oscillatorfrequency is determined by dividing the frequency to produce the clocksignal. Optionally, the method further comprises using the clock signalto drive the analog to digital converter clock signal. Optionally, theat least one amplifier comprises the second oscillator, the analog todigital converter coupled to the second oscillator and configured todigitize the captured EEG signals, and a microcontroller configured tocontrol the frequency of the second oscillator and an operation of theanalog to digital converter based on the synchronizing signal.Optionally, the microcontroller comprises a signal isolator wherein thesignal isolator comprises isolated DC-DC power converters.

Optionally, the method further comprises transmitting the amplified EEGsignals to a computing device, wherein the computing device isconfigured to process the amplified EEG signals.

Optionally, the synchronizing signal has a frequency of 1 Hz.

Optionally, the microcontroller includes a digital to analog (DAC)converter and the microcontroller is configured to adjust the secondoscillator by setting the DAC to a corresponding voltage.

Optionally, the at least one amplifier further comprises an internaltimer having microsecond resolution and the microcontroller isconfigured to measure a period of the synchronizing signal using theinternal timer.

Optionally, the at least one amplifier further comprises a filterconfigured to filter out high frequency noise, having a value rangegreater than 2 kHz, present in an analog voltage signal from themicrocontroller output.

The present specification also discloses a system for monitoring EEGsignals comprising: a plurality of EEG sensors spatially positioned on alayer of tissue for capturing EEG signals of a patient; a plurality ofamplifiers coupled with the EEG sensors for amplifying the capturedsignals; and a low frequency oscillator; wherein each amplifiercomprises: an input for receiving a low frequency synchronizing signalfrom the low frequency oscillator wherein the low frequencysynchronizing signal is configured to be distributed to each amplifierof the plurality of amplifiers; a voltage controlled oscillator; ananalog to digital converter coupled with the voltage controlledoscillator for digitizing the captured signals; and a microcontrollerfor controlling a frequency of the voltage controlled oscillator andoperation of the analog to digital converter (ADC) based on thesynchronizing signal.

The system may be used to monitor intracranial EEG signals.

Optionally, the system further comprises a computing device in datacommunication with the plurality of amplifiers for processing theamplified signals. Optionally, the system further comprises a display indata communication with the computing device for displaying theamplified signals.

Optionally, the input comprises a signal isolator for receiving thesynchronizing signal. The signal isolator may comprise isolated DC-DCpower converters.

Optionally, the synchronizing signal has a frequency of 1 Hz.

Optionally, the microcontroller includes an internal digital to analog(DAC) converter wherein the microcontroller is configured to adjust thevoltage controlled oscillator by setting the internal DAC to acorresponding voltage.

Optionally, each amplifier further comprises an internal timer withmicrosecond resolution wherein the microcontroller is configured tomeasure the period of the synchronizing signal using the internal timer.

Optionally, each amplifier further comprises a low pass filterconfigured to filter out high frequency noise on analog voltage from themicrocontroller output.

The present specification also discloses a method for synchronizing EEGsignals measured by a an EEG monitoring system, wherein the EEGmonitoring system comprises a plurality of EEG sensors spatiallypositioned on a layer of tissue for capturing EEG signals of a patient,a plurality of amplifiers coupled with the EEG sensors for amplifyingthe captured signals, and a low frequency oscillator, wherein eachamplifier comprises: an input for receiving a low frequencysynchronizing signal from the low frequency oscillator wherein the lowfrequency synchronizing signal is configured to be distributed to eachamplifier of the plurality of amplifiers; a voltage controlledoscillator; an analog to digital converter coupled with the voltagecontrolled oscillator for digitizing the captured signals; and amicrocontroller for controlling a frequency of the voltage controlledoscillator and operation of the analog to digital converter (ADC) basedon the synchronizing signal, the method comprising: distributing a lowfrequency synchronizing signal from the low frequency oscillator to eachof the plurality of amplifiers; measuring a period of the low frequencysynchronizing signal; adjusting the voltage controlled oscillator of anamplifier of the plurality of amplifiers to match a timer count based onthe period of the low frequency synchronizing signal; dividing a voltagecontrolled oscillator frequency to produce analog to digital converterclock and convert start signals; and adjusting the frequency of eachvoltage controlled oscillator of each of the plurality of amplifierssuch that the frequency of each voltage controlled oscillator isidentical.

The method may be used to monitor intracranial EEG signals.

Optionally, the EEG monitoring system further comprises a computingdevice in data communication with the plurality of amplifiers forprocessing the amplified signals. Optionally, the EEG monitoring systemfurther comprises a display in data communication with the computingdevice for displaying the amplified signals.

Optionally, each input comprises a signal isolator for receiving thesynchronizing signal. The signal isolator may comprise isolated DC-DCpower converters.

Optionally, the synchronizing signal has a frequency of 1 Hz.

Optionally, the microcontroller includes an internal digital to analog(DAC) converter wherein the microcontroller is configured to adjust thevoltage controlled oscillator by setting the internal DAC to acorresponding voltage.

Optionally, each amplifier further comprises an internal timer withmicrosecond resolution wherein the microcontroller is configured tomeasure the period of the synchronizing signal using the internal timer.

Optionally, each amplifier further comprises a low pass filterconfigured to filter out high frequency noise on analog voltage from themicrocontroller output.

The aforementioned and other embodiments of the present shall bedescribed in greater depth in the drawings and detailed descriptionprovided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present specificationwill be further appreciated, as they become better understood byreference to the following detailed description when considered inconnection with the accompanying drawings:

FIG. 1 shows a block diagram of a conventional medical system comprisinga large number of electrodes deployed on a patient body;

FIG. 2 illustrates an electroencephalography (EEG) system for detecting,diagnosing, or predicting neurological events from EEG signals, inaccordance with some embodiments of the present specification;

FIG. 3 is a block diagram illustrating an amplifier used for amplifyingEEG signals recorded from a patient's brain, in accordance with anembodiment of the present specification;

FIG. 4A is a block diagram illustrating a system comprising a pluralityof amplifiers synchronized operatively for amplifying EEG signalsrecorded from a patient's brain, in accordance with an embodiment of thepresent specification;

FIG. 4B illustrates a block diagram of an EEG system incorporating aplurality of amplifiers, in accordance with an embodiment of the presentspecification; and

FIG. 5 is a flowchart illustrating the steps involved in a method ofdistributing a low frequency signal to a plurality of synchronizedamplifiers to measure EEG signals, in accordance with an embodiment ofthe present specification.

DETAILED DESCRIPTION

The present specification enables synchronization of EEG data betweentwo or more amplifiers using a low frequency synchronizing signal thatis shared using low power circuits and standard cables. By using themethod of the present specification, electromagnetic interferences arefiltered out since the frequencies of the low speed shared signal and ofthe interferences do not overlap.

In various embodiments, the present specification provides a simple andlow cost method of synchronizing the data acquisition of multipleamplifiers during EEG monitoring. This method eliminates the need fordistributing data from a high speed clock to each of the multipleamplifiers, thereby eliminating the need for high power consumption andspecialized components/cables.

In an embodiment, the method of the present specification comprisesdistributing a low frequency clock among a plurality of amplifiers forsynchronizing the data acquired by said amplifiers during EEGmonitoring. The low frequency clock uses single ended circuitry andcabling whereby high frequency electromagnetic interference can befiltered out from the clock signal.

In various embodiments, the methods and systems of the presentspecification enable the synchronizing of a sample rate of EEG dataacquired on different devices (amplifiers) with only a low frequencysynchronizing signal. In some embodiments, a low frequency synchronizingsignal is transmitted to the devices to be synchronized, wherein theterm low frequency, in the context of a synchronizing signal, refers toa range of 0.1 Hz to 10 kHz, with a preferred range of 0.5 Hz to 2 Hz.It should be appreciated that the 0.5 Hz to 2 Hz range leads to a moreaccurate synchronization process. Each device measures the period of thesynchronizing signal using an internal timer with microsecondresolution. The device then adjusts its microcontroller clock so thatthe expected number of ticks occurs between the low frequencysynchronizing signal edges (for example, 1,000,000). This is done byadjusting the voltage to an external voltage-controlled oscillator infinite steps using a digital to analog converter (DAC) internal to themicrocontroller. These adjustments can continue, to counter clock driftover time, in order to maintain synchronization.

A “computing device” is at least one of a cellular phone, PDA, smartphone, tablet computing device, patient monitor, custom kiosk, or othercomputing device capable of executing programmatic instructions. Itshould further be appreciated that each device and monitoring system mayhave wireless and wired receivers and transmitters capable of sendingand receiving data. Each “computing device” may be coupled to at leastone display, which displays information about the patient parameters andthe functioning of the system, by means of a GUI. The GUI also presentsvarious menus that allow users to configure settings according to theirrequirements. The system further comprises at least one processor tocontrol the operation of the entire system and its components. It shouldfurther be appreciated that the at least one processor is capable ofprocessing programmatic instructions, has a memory capable of storingprogrammatic instructions, and employs software comprised of a pluralityof programmatic instructions for performing the processes describedherein. In one embodiment, the at least one processor is a computingdevice capable of receiving, executing, and transmitting a plurality ofprogrammatic instructions stored on a volatile or non-volatile computerreadable medium. In addition, the software comprised of a plurality ofprogrammatic instructions for performing the processes described hereinmay be implemented by a computer processor capable of processingprogrammatic instructions and a memory capable of storing programmaticinstructions.

“Electrode” refers to a conductor used to establish electrical contactwith a nonmetallic part of a circuit such as a patient's body. EEGelectrodes are small metal discs, grids, strips or cylinders usuallymade of stainless steel, platinum, tin, gold or silver covered with asilver chloride coating. They are typically placed on the scalp onpredetermined locations but may also be placed as intracranialelectrodes directly on the surface of the brain or implanted into thebrain to record electrical activity from the cerebral cortex.

An “electrode grid” is a thin sheet of material with multiple small(roughly a couple mm in size) recording electrodes implanted within it.These are placed directly on the surface of the brain and have theadvantage of recording the EEG without the interference of the skin, fattissue, muscle, and bone that may limit scalp EEG. Shapes and sizes ofthese sheets are chosen to best conform to the surface of the brain andthe area of interest.

A “depth electrode” refers to small wires that are implanted within thebrain itself. Each wire has electrodes which surround it. Theseelectrodes are able to record brain activity along the entire length ofthe implanted wire. They have the advantage of recording activity fromstructures deeper in the brain. They can be implanted through small skinpokes.

The present specification is directed towards multiple embodiments. Thefollowing disclosure is provided in order to enable a person havingordinary skill in the art to practice the invention. Language used inthis specification should not be interpreted as a general disavowal ofany one specific embodiment or used to limit the claims beyond themeaning of the terms used therein. The general principles defined hereinmay be applied to other embodiments and applications without departingfrom the spirit and scope of the invention. Also, the terminology andphraseology used is for the purpose of describing exemplary embodimentsand should not be considered limiting. Thus, the present invention is tobe accorded the widest scope encompassing numerous alternatives,modifications and equivalents consistent with the principles andfeatures disclosed. For purpose of clarity, details relating totechnical material that is known in the technical fields related to theinvention have not been described in detail so as not to unnecessarilyobscure the present invention.

In the description and claims of the application, each of the words“comprise” “include” and “have”, and forms thereof, are not necessarilylimited to members in a list with which the words may be associated. Itshould be noted herein that any feature or component described inassociation with a specific embodiment may be used and implemented withany other embodiment unless clearly indicated otherwise.

As used herein, the indefinite articles “a” and “an” mean “at least one”or “one or more” unless the context clearly dictates otherwise.

FIG. 1 shows a block diagram of a conventional medical system 100comprising a large number of electrodes deployed on the body of apatient 102. The medical device 101 represents a conventionalneuromonitoring medical system, such as an EEG (electroencephalography)system, which comprises a large number of electrodes for monitoring aneurological state of a patient for diagnosis and preventive treatmentof certain diseases and for monitoring patients during anesthesia, amongother procedures. As shown in FIG. 1 , the medical device 101 is coupledto the patient 102 through a plurality of electrical leads 103 such thateach of the leads 103 is coupled to an electrode (not shown) positionedat an appropriate location on the body of the patient 102.

FIG. 2 illustrates an electroencephalography (EEG) system 200 fordetecting, diagnosing, or predicting neurological events from EEGsignals, in accordance with some embodiments of the presentspecification. The figure shows a plurality of EEG sensors or electrodes205 spatially positioned on a layer of tissue such as the scalp of apatient 215. In other embodiments, the plurality of electrodes ispositioned intracranially, directly on the brain. For example, in someembodiments, the plurality of electrodes is placed on the brain by skullresection or via burr holes. The plurality of electrodes 205 areelectrically connected with a multi-channel amplifier 220 that is indata communication with a computing device 240. The computing device 240is in data communication with a display unit 230 and at least onedatabase 235.

In various embodiments, the plurality of electrodes 205 are small metaldiscs, strips, grids, and/or cylinders typically made of stainlesssteel, platinum, tin, gold or silver covered with a silver chloridecoating. The plurality of electrodes 205 sense electrical signals (EEGsignals) from the patient's brain and conduct the analog signals over anelectrical connection link to the multi-channel amplifier 220 thatamplifies the signals, converts the signals from an analog EEG data setto a digital EEG data set, and communicates the resultant digital EEGsignal to the computing device 240 over a communication link. Inembodiments, the communication link may be wired or wireless links. Invarious embodiments, more than one amplifier 220 may be used foracquiring and amplifying the voltage sensed by the electrodes 205 in theEEG system.

The computing device 240 includes an input/output controller, at leastone communications interface and system memory. The system memoryincludes at least one random access memory (RAM) and at least oneread-only memory (ROM). These elements are in communication with acentral processing unit (CPU) to enable operation of the computingdevice 240. In various embodiments, the computing device 240 may be aconventional standalone computer or alternatively, the functions of thecomputing device 240 may be distributed across multiple computer systemsand architectures. For example, in a distributed architecture, the atleast one database 235 and processing circuitry are housed in separateunits or locations. Some units perform primary processing functions andcontain at a minimum a general controller or a processing circuitry anda system memory.

The computing device 240 executes EEG software 245 that implements aplurality of programmatic instructions or code to process, store,retrieve and display, on the display unit 230, the patient's EEG data.In embodiments, the EEG software 245 processes the received digital EEGsignals, extracts parameters that characterize the EEG data, andgenerates a display of the data for a user. The processed EEG data iseither displayed on the display unit 230 in real-time or stored in atleast one database 235 for later analyses.

In some embodiments, execution of sequences of programmatic instructionsenables or causes the CPU to perform various functions and processes. Inalternate embodiments, hard-wired circuitry may be used in place of, orin combination with, software instructions for implementation of theprocesses of systems and methods described in this specification. Thus,the systems and methods described are not limited to any specificcombination of hardware and software.

FIG. 3 is a block diagram illustrating an amplifier 300 used foramplifying EEG signals recorded from a patient's brain, in accordancewith an embodiment of the present specification. The amplifier 300comprises a microcontroller 302, a voltage controlled oscillator 304, ananalog-to-digital converter (ADC) 306 and a low pass filter 308. Asshown, EEG analog signals 310 recorded from a patient's brain by using aplurality of EEG electrodes are transmitted to the ADC 306 whichconverts the input analog signals to digital signals for output to themicrocontroller 302. The microcontroller 302 controls the operation ofthe voltage controlled oscillator 304 by controlling the voltage on theDAC output 307, thereby adjusting the frequency of the voltagecontrolled oscillator 304 to a predefined frequency. More specifically,the microcontroller 302, at the DAC output 307, modulates the voltageamplitude and/or frequency which, in turn, controls the frequency atwhich the voltage controlled oscillator 304 oscillates. Themicrocontroller 302 controls the ADC 306 by generating the clock andstart signals of the ADC 306. The microcontroller 302 bases the controlof the voltage control oscillator 304 and the ADC 306 on the inputtimer/frequency 301. The low pass filter 308 filters out high frequencynoise above 2 kHz on the analog voltage from the microcontroller DACoutput 307 so as to provide a useful DC signal input 311 to theoscillator 304 thereby enabling the oscillator 304 to produce a stableoscillator frequency at an oscillator (OSC) input 309 of themicrocontroller 302.

FIG. 4A is a block diagram illustrating a system 400 comprising aplurality of amplifiers synchronized operatively for amplifying EEGsignals recorded from a patient's brain, in accordance with anembodiment of the present specification. Each of the plurality ofamplifiers 402 a through 402 n comprises a signal isolator 405, amicrocontroller 406, a voltage controlled oscillator 408, an analog todigital converter 410 and a low pass filter 412. As shown, a lowfrequency oscillator 401 provides a low frequency synchronizing signalwhich is distributed to each of the plurality of amplifiers 402 athrough 402 n that operate in conjunction to amplify and digitizeintracranial EEG signals. In some embodiments, the synchronizing signalhas a frequency in a range of 0.1 Hz to 10 kHz, more preferably in arange of 0.5 Hz to 2 Hz, and most preferably around 1 Hz.

In some embodiments, the low frequency oscillator 401 is external to theamplifiers 402 a through 402 n. Each signal isolator 405, associatedwith each of the plurality of amplifiers 402 a through 402 n,electrically isolates each of the plurality of amplifiers 402 a through402 n from ground. In some embodiments, each signal isolator 405comprises isolated DC-DC power converters and provides an isolationbarrier over which a low frequency signal can be easily coupled. Eachvoltage controlled oscillator 408 provides a master clock to themicrocontroller 406 of its respective amplifier. In various embodiments,any synchronizing signal frequency may be provided by the low frequencyoscillator 401. However, a synchronizing signal frequency lower than 1Hz increases the time taken to synchronize the signal while asynchronizing signal frequency higher than 1 Hz requires moremicrocontroller resources.

In embodiments, cables 403 are used to supply the synchronizing signalfrom the low frequency oscillator 401 to each of the plurality ofamplifiers 402 a through 402 n. In an embodiment, the synchronizingsignal is carried by a 28 AWG cable/conductor. In alternate embodiments,cables having other AWG values may also be used.

During operation, a microcontroller 406 of each of the amplifiers 402 athrough 402 n receives the 1 Hz synchronizing signal from the lowfrequency oscillator 401 via a timer input 407 and measures the periodof the 1 Hz synchronizing signal using an internal timer. In someembodiments, the internal timer measures the period of the 1 Hzsynchronizing signal with microsecond resolution. The microcontroller406 then adjusts an operational frequency of the voltage controlledoscillator 408 by setting its internal DAC to a voltage value within apredefined range until the measured period of the synchronizing signalat timer input 407 matches a defined timer count based on the expectedperiod of the synchronizing signal.

In some embodiments, the synchronization signal is a square wave with afrequency of 1 Hz and 50% duty cycle (high for half of the period, lowfor half of the period). The square wave is defined by “signal edges”referring to the rising edges of the square wave. Alternatively, “signaledges” may also refer to the falling edges of the square wave. Inembodiments, one million “ticks” occur in a timer since a previous 1 Hzsync edge. In embodiments, if a timer is operated with microsecondresolution and the value of the timer is captured at each rising edge ofthe 1 Hz synchronization signal, one would expect a delta of 1,000,000between consecutive timer captures since there are 1,000,000microseconds in 1 second (1 Hz). Since the voltage controlled oscillator408 is providing the master clock to the microcontroller 406, adjustingthe operational frequency of the voltage controlled oscillator 408 willadjust the frequency of all microcontroller clocks and timing signalsproduced by the microcontroller 406. The microcontroller 406 adjusts theoperational frequency of the voltage controlled oscillator 408 bysetting the internal DAC of the microcontroller 406 to a certain voltagevalue which is then sent to the voltage controlled oscillator 408 by themicrocontroller 406. In embodiments, to maintain synchronization, theadjustments of the operational frequency of the voltage controlledoscillator 408 continue as the clocks drift over time and temperature.In some embodiments, the internal DAC of the microcontroller 406 is setto a voltage value in a range of 0 to 3.3 V.

Thereafter, the operational frequency of the voltage controlledoscillator 408 is divided by the microcontroller 406 to produce clockand ‘convert start’ signals of the analog to digital converter (ADC)410. Both the clock and ‘convert start’ signals determine the samplerate and timing of the analog to digital conversion within the ADC 410.Thus, the ADC 410 is synchronized to the 1 Hz signal.

Each microcontroller 406 in each of the other amplifiers 402 n adjuststhe frequency of its associated voltage controlled oscillator so thatits frequency is identical to the frequency of the voltage controlledoscillator 408. In some embodiments, the voltage controlled oscillator408 can be adjusted after multiple 1 Hz synchronizing signal periods orat any other frequency interval that results in a desired accuracy ofsynchronization of the amplifiers. For example, in an embodiment, themicrocontroller 406 counts, using its internal timer, the number ofmicrosecond ticks that occur over four 1 Hz synchronizing signal periodsand adjust its clock until it reaches the desired count. This allows forgreater accuracy of synchronization but with a tradeoff of more timeelapsed to reach synchronization.

Without the voltage controlled oscillator 408, the use of low frequencysynchronizing signal is restricted to an accuracy of approximately 10μsec of synchronization using calculations done on a host PC system fortime-stamped data and stimulations. The microcontroller clocks areallowed to drift in this timing scheme with the host PC correcting thetimestamps for the calculated drift. With the addition of the voltagecontrolled oscillator 408 and the method of measuring and compensatingfor oscillator inaccuracy, synchronization better than 1 μsec isachieved at the microcontroller clock level. This tighter frequencyaccuracy is necessary to avoid beat frequencies.

FIG. 4B illustrates a block diagram of an EEG system incorporating aplurality of amplifiers, in accordance with an embodiment of the presentspecification. Referring to FIG. 4B, a plurality of 128 channelamplifiers 450 receive input EEG signals via 128×4 electrode wirescaptured by a plurality of electrodes 452 connected to a patient.Digitized and amplified signals travel via a plurality of power/signalsynchronization cables 454 between each of the plurality of amplifiers450. A first power/signal synchronization cable 455 carries thedigitized and amplified signal communicated between each of theplurality of amplifiers 450 to a power unit comprising a low frequencyoscillator 456 which is used to synchronize the signals received fromthe plurality of amplifiers 450. The synchronized signals aretransferred via data cables 458 to a computing device 460 (similar tocomputing device 240 described with reference to FIG. 2A) and aredisplayed for analysis on a display device 462 coupled with thecomputing device 460.

FIG. 5 is a flowchart illustrating a plurality of exemplary stepsinvolved in a method of distributing a low frequency signal to aplurality of amplifiers for synchronization and to measure EEG signals,in accordance with an embodiment of the present specification. At step502, a low frequency oscillator of an EEG monitoring system of thepresent specification distributes a low frequency synchronizing signalto a plurality of amplifiers that are in data communication with the lowfrequency oscillator. In some embodiments, the low frequencysynchronizing signal is a 1 Hz synchronizing signal.

At step 504, a microcontroller in each of the plurality of amplifiersmeasures a period of the low frequency synchronizing signal using aninternal timer. In some embodiments, the internal timer measures theperiod of the low frequency synchronizing signal with microsecondresolution. The microcontroller then adjusts an operational frequency ofa voltage controlled oscillator of the amplifier by setting an internalDAC of the microcontroller to a voltage value, at step 506, until themeasured period of the low frequency synchronizing signal matches atimer count based on the expected period of the low frequencysynchronizing signal. At step 508, the microcontroller sends the voltagevalue of the internal DAC to the voltage controlled oscillator to enablethe voltage controlled oscillator to produce a stable frequency to at anoscillator (OSC) input of the microcontroller.

At step 510, the adjusted operational frequency of the voltagecontrolled oscillator is divided by the microcontroller to produce clockand convert start signals of an analog to digital converted (ADC) of theamplifier. Finally, at step 512, each microcontroller in each of theother amplifiers (of the plurality of amplifiers) adjusts the frequencyof its associated voltage controlled oscillator so that the frequency ofeach voltage controlled oscillator of each amplifier of the plurality ofamplifiers is identical. In some embodiments, the frequency adjustmentoccurs at twice the low frequency synchronizing signal or at anyinterval that will result in the desired accuracy of synchronization ofthe amplifiers.

The above examples are merely illustrative of the many applications ofthe system and method of present specification. Although only a fewembodiments of the present specification have been described herein, itshould be understood that the present specification might be embodied inmany other specific forms without departing from the spirit or scope ofthe specification. Therefore, the present examples and embodiments areto be considered as illustrative and not restrictive, and thespecification may be modified within the scope of the appended claims.

We claim:
 1. A method for synchronizing EEG signals measured by an EEG monitoring system, wherein the EEG monitoring system comprises a plurality of EEG sensors positioned on a layer of tissue and wherein each of the plurality of EEG sensors is configured to capture EEG signals of a patient, at least one amplifier coupled to each of the plurality of EEG sensors and configured to amplify the captured EEG signals, and a first oscillator, wherein the at least one amplifier comprises an input for receiving a synchronizing signal from the first oscillator, the method comprising: distributing the synchronizing signal from the first oscillator to each of the at least one amplifier; measuring a period of the synchronizing signal; adjusting a second oscillator, having a frequency, in the at least one amplifier to match a timer count based on the period of the synchronizing signal; determining a function of the frequency of the second oscillator frequency to produce a clock signal; and adjusting a frequency of each of the second oscillators such that the frequencies of the second oscillators are identical.
 2. The method of claim 1, wherein the first oscillator is configured to generate the synchronizing signal having a frequency in a range of 0.1 Hz to 10 kHz.
 3. The method of claim 1, wherein the second oscillator is voltage controlled.
 4. The method of claim 1, wherein the function of the frequency of the second oscillator frequency is determined by dividing the frequency to produce the clock signal.
 5. The method of claim 4, further comprising using the clock signal to drive the analog to digital converter clock signal.
 6. The method of claim 4, wherein the at least one amplifier comprises the second oscillator, the analog to digital converter coupled to the second oscillator and configured to digitize the captured EEG signals, and a microcontroller configured to control the frequency of the second oscillator and an operation of the analog to digital converter based on the synchronizing signal.
 7. The method of claim 6, wherein the microcontroller comprises a signal isolator and wherein the signal isolator comprises isolated DC-DC power converters.
 8. The method of claim 1, further comprising transmitting the amplified EEG signals to a computing device, wherein the computing device is configured to process the amplified EEG signals.
 9. The method of claim 1, wherein the synchronizing signal has a frequency of 1 Hz.
 10. The method of claim 1, wherein the microcontroller includes a digital to analog (DAC) converter and wherein the microcontroller is configured to adjust the second oscillator by setting the DAC to a corresponding voltage.
 11. The method of claim 1, wherein the at least one amplifier further comprises an internal timer having microsecond resolution and wherein the microcontroller is configured to measure a period of the synchronizing signal using the internal timer.
 12. The method of claim 1, wherein the at least one amplifier further comprises a filter configured to filter out high frequency noise, having a value range greater than 2 kHz, present in an analog voltage signal from the microcontroller output. 